"They're over," a source tells PEOPLE about the short-lived relationship. "It ended last month."

No reason was given for a split, and the stars reps didn't have immediate comment, but the two spent the holidays – and their birthdays – apart.

Swift, 21, rang in 2011 in Nashville, solo, at a party, while Gyllenhaal, 30, was in New York, where he attended a closing party for Broadway's Fela! on Jan. 2. While in the Big Apple, Gyllenhaal was also spotted dining with his mother at the Spotted Pig.